SUPPOSE THAT JUST after you finish reading this article, you keel over, dead. Perhaps you’re ready for such an eventuality, in that you have prepared a will or made some sort of arrangement for the fate of the worldly goods you leave behind: financial assets, personal effects, belongings likely to have sentimental value to others, and artifacts of your life like photographs, journals, letters. Even if you haven’t made such arrangements, all of this will get sorted one way or another, maybe in line with what you would have wanted, and maybe not.

But many of us, in these worst of circumstances, would also leave behind things that exist outside of those familiar categories. Suppose you blogged or tweeted about this article, or dashed off a Facebook status update, or uploaded a few snapshots from your iPhone to Flickr, and then logged off this mortal coil. It’s now taken for granted that the things we do online are reflections of who we are or announcements of who we wish to be. So what happens to this version of you that you’ve built with bits? Who will have access to which parts of it, and for how long?

For most of us, the fate of tweets and status updates and the like may seem trivial (who cares—I’ll be dead!). But increasingly we’re not leaving a record of life by culling and stowing away physical journals or shoeboxes of letters and photographs for heirs or the future. Instead, we are, collectively, busy producing fresh masses of life-affirming digital stuff: 5 billion images and counting on Flickr; hundreds of thousands of YouTube videos uploaded every day; oceans of content from 20 million bloggers and 500 million Facebook members; 2 billion tweets a month. Sites and services warehouse our musical and visual creations, personal data, shared opinions, and taste declarations in the form of reviews and lists and ratings, even virtual scrapbook pages. Avatars left behind in World of Warcraft or Second Life can have financial or intellectual-property holdings in those alternate realities.

One estimate pegs the number of U.S. Facebook users who die annually at something like 375,000. Academics have begun to explore the subject (how does this change the way we remember and grieve?), social-media consultants have begun to talk about it (what are the legal implications?), and entrepreneurs are trying to build whole new businesses around digital-afterlife management (is there a profit opportunity here?). Evan Carroll and John Romano, interaction-design experts in Raleigh, N.C., who run a site called TheDigitalBeyond​.com, have just published a tips-and-planning book, Your Digital Afterlife, with advice about such matters as appointing a “digital executor.”

ON OCT. 18, 2009, Mac Tonnies updated his blog, sent out some public tweets and private messages via Twitter, went to bed, and died of cardiac arrhythmia. While he had experienced some symptoms that indicated potential heart problems, his sudden death came as a shock even to those who knew him well. He was 34.

Tonnies lived in Kansas City, Mo. He was single and childless, owned two cats, and paid his bills through workaday jobs, behind the counter at Starbucks or doing phone work for a small marketing agency. He was also a writer (he had just finished a draft of his third book) with an adventurous intellect. His audience was small but devoted. Tonnies, who started his blog, Posthuman Blues, in 2003, was an extremely active user of online media and forged many friendships with people he never met in the physical world. Many of his interests were distinctly future-oriented, a freewheeling consideration of the very nature of humanity.

Rita J. King, an expert on online identity and persona who is an “innovator in residence” for IBM, was introduced to Tonnies via e-mail in 2004, and they kept in frequent touch. “He is the one I had all my conversations with, early on, about technology and consciousness,” she says.

The last entry on Posthuman Blues was titled “Triptych #15,” a set of three images with no text. The first comment to this post came from an anonymous reader, wondering why Tonnies had not updated the blog or tweeted for two days. Some similar comments followed, and then this: “Mac Tonnies passed away earlier in the week. Our condolences are with his family and friends in this time of grief.” The author of that comment was also anonymous. After a rapid back-and-forth about whether this startling news was true and some details of the circumstances, that post’s comment section transformed into a remarkable mix of tributes, grieving, and commiseration. You can still read all this today, in a thread that runs to more than 250 comments.

“It was a very strange feeling,” Dana Tonnies, Mac’s mother, told me, describing how she and her husband became aware of the swirl of activity attaching to her son’s online self. “I had no control over what was being said about him, almost immediately.” Dana and Bob Tonnies were close to their only son—in fact they had coffee with him, in a regular Sunday ritual, the morning before he died—but they had little contact with his digital self.

Dana is presently going through Posthuman Blues, in order, from the beginning. “I still have a year to go,” she says. Reading it has been “amazing,” she continues—funny posts, personal posts, poetic posts, angry posts about the state of the world. I ask her if what she is reading seems like a different, or specifically narrow, version of her son. “Oh, no, it’s him,” she says. “I can hear him when I read it.”

I spoke to a half-dozen people Mac Tonnies met online and in some cases never encountered in the physical world. Each expressed a genuine sense of loss; a few sounded grief-stricken even more than a year later. Mark Plattner, who lives in St. Louis and met Tonnies a dozen years ago through the comments section of another blog, decided that Posthuman Blues needed to survive. He used software called Sitesucker to put a backup of the entire thing—pictures, videos, links included—on a hard drive. In all, Plattner has about 10 gigabytes of material, offering a sense of Tonnies’ “personality and who he was,” Plattner says. “That’s what we want to remember.”

This outpouring of digital grief, memorial-making, documentation, and self-expression is unusual, maybe unique, for now, because of the kind of person Tonnies was and the kinds of friends he made online. But maybe, his friend Rita King suggests, his story is also a kind of early signal of one way that digital afterlives might play out. And she doesn’t just mean this in an abstract, scholarly way. “I find solace,” she told me, “in going to Mac’s Twitter feed.”

SURVIVORS MAY NOT be aware of the deceased’s full digital hoard, or they may not have the passwords to access the caches they do know about. They may be uncertain to the point of inaction about how to approach the problem at all.

This has inspired a variety of entrepreneurs to place bets that, eventually, people will want control over the afterlife of their digital selves. Several promise to manage the details of your digital death—storing your passwords and your wishes for who gets access to what and integrating your content-related instructions into a kind of adjunct to a traditional will. Legacy Locker claims “around 10,000” people have signed up for its digital-estate-management service.

My favorite digital-mortality business,, gives the idea of speaking from beyond the grave a Web-era update. DeathSwitch was founded in 2006 by the neuroscientist and writer David Eagleman to coincide with a short story he wrote for Nature, titled “A Brief History of Death Switches.” The story imagines an automated service that allowed its users to send messages after they die. People use it to reveal secret bank accounts to heirs, confess to sins, or settle scores from beyond the grave. Over time, uses for this fictional death switch become so elaborate that it is hard to tell that the sender of the message is deceased.

That last part hasn’t happened yet, but otherwise the service offered by DeathSwitch​.com, in real life, is basically the same as the fictional one: some final words from you, to whomever, after you’ve gone.

MAC TONNIES’ MANY eclectic intellectual pursuits included at least a passing interest in the notion of cyberimmortality. The idea of the self escaping bodily death by transforming into an age-proof, sickness-proof essence that can be uploaded into a computer or network dates back at least to Vernor Vinge’s 1981 novella True Names. A year after that, William Gibson gave us the word “cyberspace” to describe a new place where humans might exist, potentially forever, outside the physical world.

By the 1990s, as the Internet became a familiar presence in many people’s lives, some began to suggest that this was no mere science-fiction scenario; it was the future. Vinge was among those (along with, notably, Ray Kurzweil) to discuss the transformation of humans by technology, coming in a matter of decades, referred to as “the singularity.”

The Carnegie Mellon robotics expert Hans Moravec, the artificial-intelligence pioneer Marvin Minsky, the computer scientist Rudy Rucker, and others articulated visions of a future in which technology might truly free us from “the bloody mess of organic matter,” to use a phrase of Minsky’s. In her 1999 book, The Pearly Gates of Cyberspace, Margaret Wertheim contextualized such speculations as attempts to, in effect, “construct a technological substitute for the Christian space of heaven.”

Wertheim pointed out that cyberspace had become a new kind of place, where alternate (or at least carefully curated or burnished) identities could be forged, outside the familiar boundaries of the physical world, like the body and geography. It’s not such a long journey to follow those assertions to the “view that man is defined not by the atoms of his body but by an information code,” as Wertheim wrote. “This is the belief that our essence lies not in our matter but in a pattern of data.” She called this idea the “cybersoul,” a “posited immortal self, this thing that can supposedly live on in the digital domain after our bodies die.”

I found myself wondering about what Mac Tonnies’ take on all this might be. The last of his friends to whom I spoke was Paul Kimball, a filmmaker who lives in Nova Scotia. He met Tonnies online about a decade ago; among their shared interests, it turns out, was the relationship among technology, consciousness, and mortality.

The day before we spoke, Kimball continued, he had linked to an old Posthuman Blues post on his Facebook page, seeking reactions from his own online circle. “So I’m still having this conversation” with Tonnies, he told me, “even though he’s been dead for more than a year.” Eventually, Kimball added, such situations may be routine. “We’re entering a world where we can all leave as much of a legacy as George Bush or Bill Clinton. Maybe that’s the ultimate democratization,” he said. “It gives all of us a chance at immortality.”

After talking to Kimball, I ended up watching a couple of interview clips of Tonnies on YouTube. “I like to think of death as a glorified terminal illness,” Mac Tonnies said, and will continue to say, for as long as this particular collection of bits remains available for someone to watch and listen to. “If we can escape the boundaries of death,’’ Tonnies said—says—“maybe we’ll be OK.”

Rob Walker is the author of Buying In. This story originally appeared in The New York Times Magazine. Used with permission. All rights reserved.